A lithium ion electrolytic cell, such as a rechargeable lithium ion battery, is commonly constructed by means of the lamination of electrode and separator film cell elements which are individually prepared. Each of the electrodes and the film separator is formed individually, for example by coating, extrusion, or otherwise, from compositions including binder materials and a plasticizer.
Lithium ion electrolytic cells 101 may be of the traditional type, shown in FIG. 1, with an cathode 110, a separator 112, and an anode 114 sandwiched together.
A separator is positioned between a negative electrode and a positive electrode. The anode, separator, and cathode structures are then laminated to produce a standard unitary flexible electrolytic cell precursor structure. The precursor can be extracted and activated with electrolyte to form a functional battery.
A lithium ion battery typically comprises several solid, secondary electrolytic cells in which the current from each of the cells is accumulated by a conventional current collector, so that the total current generated by the battery is roughly the sum of the current generated from each of the individual electrolytic cells employed in the battery. In lithium ion batteries it is common to stack separate electrolyte cells to create the battery.
There is a trend to commercially develop "bi-cells", in which a single central electrode has two counter electrodes, one positioned on either side of the central electrode. The central electrode has been an anode, the counter electrodes have been cathodes. Bi-cells are more complex than standard cells, and require the successful lamination of more layers.
A bi-cell 201, for example that shown in FIG. 2a, includes, sequentially, a first counter electrode 214a having a first medially positioned current collector 215a, a first separator 212a, a central electrode 210 having a centrally located current collector 211, a second separator 212b, and a second counter electrode 214b having a second medially positioned current collector 215b. An electrode tab (not shown) connects the central electrode elements to the exterior of the package. A similar counter electrode tab (not shown) connects the counter electrode elements to the exterior of the package.
Lamination has been, and continues to be, a problem in the preparation of polymer batteries. FIG. 2b shows an exploded graphic representation of the interface a current collector. The current collectors used are grids or perforated sheets 255, which permit a direct contact interface region 248 between two sheets of polymer electrode 253a, 253b. This electrode--electrode contact across the perforated current collector has proven to be critical in producing bi-cells which resist delamination during use.
It is preferred that a battery achieve the maximum energy potential and cycle life. It would therefore be preferred that the current collector in the anodic and cathodic electrode be positioned to provide optimum battery performance.